The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Counterfeit pills may have killed Prince: report

Investigators looking into pop legend Prince's death believe that counterfeit pills may have killed him, a report said Monday.

The Star Tribune, the daily newspaper in Prince's hometown of Minneapolis, said that authorities turned to the theory after seizing pills from Prince's Paisley Park estate.

The confiscated pills were marked as hydrocodone, a commonly prescribed drug for moderate pain relief, but in fact contained fentanyl, an intensely powerful painkiller for which Prince had no prescription.

An autopsy earlier found that Prince died on April 21 from an accidental overdose of fentanyl but did not address how he obtained the drug.

The Star Tribune, which quoted an anonymous source, said that investigators were "leaning toward the theory that he took the pills not knowing they contained the drug."

Prince was found dead in his Paisley Park estate just as he prepared to discuss treatment with a California expert in painkiller addiction.

The 57-year-old "Purple Rain" star was outwardly a model of health who was known to be conscientious in his food choices and critical of musicians who abused drugs.